Android開發——淺談onInterceptTouchEvent、onTouchEvent與onTouch

一、onTouch

onTouch是View中OnTouchListener接口中的方法，處理View及其子類被touch是的事件處理。當然，前提是touch時間能夠傳遞到指定的view。Q1：為什麼會傳遞不到呢？

   1: 　　/**

   2:      * Interface definition for a callback to be invoked when a touch event is

   3:      * dispatched to this view. The callback will be invoked before the touch

   4:      * event is given to the view.

   5:      */

   6:     public interface OnTouchListener {

   7:         /**

   8:          * Called when a touch event is dispatched to a view. This allows listeners to

   9:          * get a chance to respond before the target view.

  10:          *

  11:          * @param v The view the touch event has been dispatched to.

  12:          * @param event The MotionEvent object containing full information about

  13:          *        the event.

  14:          * @return True if the listener has consumed the event, false otherwise.

  15:          */

  16:         boolean onTouch(View v, MotionEvent event);

  17:     }

二、onTouchEvent

onTouchEvent同樣也是在view中定義的一個方法。處理傳遞到view 的手勢事件。手勢事件類型包括ACTION_DOWN,ACTION_MOVE,ACTION_UP,ACTION_CANCEL四種事件。

   1: /**

   2:  * Implement this method to handle touch screen motion events.

   3:  *

   4:  * @param event The motion event.

   5:  * @return True if the event was handled, false otherwise.

   6:  */

   7: public boolean onTouchEvent(MotionEvent event) {

   8: 　……

   9: 　……

  10: }

一旦onTouchEvent方法被調用，並返回true則這個手勢事件就結束了，並不會向下傳遞到子控件。Q2：onTouchEvent什麼時候被調用呢？

三、onInterceptTouchEvent

onInterceptTouchEvent是在ViewGroup裡面定義的。Android中的layout布局類一般都是繼承此類的。onInterceptTouchEvent是用於攔截手勢事件的，每個手勢事件都會先調用onInterceptTouchEvent。

   1: public boolean onInterceptTouchEvent(MotionEvent ev) {

   2:         return false;

   3: }

此方法返回false，則手勢事件會向子控件傳遞；返回true，則調用onTouchEvent方法。